Opinion - Your letters
Feedback: Your letters
All is not lost
Tom Jacob's argument that reducing the standard UK mains voltage would mean I2R losses in cables rising to achieve the same wattage delivered to the loads (Feedback, 8 March 2008) only holds water if the connected demand remains the same as the supplying voltage varies.
This is not the case; the response of connected demand to voltage variations will vary with the type of load. Equipment connected by a stabilised voltage source will not change its current consumption, so, for these loads, that current and losses will increase by a tiny amount.
Resistive type loads will however vary considerably. For example, the current taken by a domestic 3kW immersion heater supplied at 230V will be 13.043A and its resistance17.634 ohms. Increasing the supply voltage to 240V will increase the current to 13.61A. Energy consumption becomes 3,266W. This represents an increase in power of 8.9 per cent and an increase in current of 4.3 per cent. The transmission loss to supply this increased demand increases by 4.3 x 4.3 = 18.49 per cent, although this is 18.49 per cent of a very small number.
It is true that the heater will operate slightly longer at the lower rating to deliver the same amount of energy to the hot water tank until the thermostat switches off the load. Other resistive loads (lighting for example) will not however recover the lost energy and will make genuine total energy savings.
Fortunately the overall network demand response to voltage variation is well known. At times when connected demand exceeds available generation system voltage is reduced by 3 per cent, reducing connected demand by around 5 per cent. If demand still exceeds available generation, system voltage is reduced by a further 3 per cent. Of course the reverse argument applies: increasing the system voltage will increase the connected demand and therefore the system losses.
Of much greater significance is the increase in demand associated with the higher voltage at times of peak demands; at the winter peak demand the demand reduction increase associated with a voltage increase of 6 per cent (of about 10 per cent) equates to around 5.7GW or three power stations the size of Ratcliffe On Soar. As this demand will be met by the most expensive, and therefore likely to be the least efficient resulting in a large increase in carbon dioxide and sulphur dioxide emissions.
According to the National Grid the UK electricity system total transmission power loss is only 0.0001 per cent and around the national peak demand of 57GW this will equate to only 5.7MW. Hardly a significant number when compared with the increase in demand of 5.7GW.
Graham Thompson MIET, retired engineer, National Grid, Redditch, Worcs
Brian Ellis's comments (Feedback, 8 March 2008) on my article 'How to get 100 mpg from your car' in the 9 February 2008 issue of E&T are interesting. He is correct in concluding that the resulting savings are not great.
We have two hybrid Toyotas, one standard and the one described in the article which has an extra li-ion battery pack. The standard car does 60mpg. The converted car does 100mpg using mains electricity and petrol.
Petrol in the UK is currently just under £5/gallon. To cover 100 miles the standard car uses 1.67 gallons costing £8.35 or 8.35p/mile. To cover the same 100 miles the plug-in car uses one gallon and 12kWh of electricity. The petrol costs £5 and my night rate electricity costs 3.5p/kWh (including tax). Total cost is £5.42 or 5.42p/mile.
Savings over 1,000 miles are just under £30; not a lot. The cost savings come from the distorted tax situation. The real costs are in the initial purchase and eventual replacement of the battery pack. The 'well to wheel' argument will continue for electric cars and hybrids.
The purpose of the project was to demonstrate the relative ease at which a production hybrid can be converted to use much less fuel. Why can't the manufacturers do this now?
Jim Fell MIET, Peterborough
Sweden's wood gas cars aren't the first
Pelle Neroth ('Northern Lights', 23 February 2008) may be interested to know that the Swedes weren't the first to use wood gas to drive vehicles during the Second World War. 'Gas producers' were developed by South Australian farmers during the 1930s to use their abundant mallee stumps to drive their Holt tractors and farm trucks.
The Cash brothers went from Eyre Peninsula to Melbourne at the beginning of the war and successfully set up manufacture. Gas producers were used widely during the war but dropped as soon as it finished as they were dirty, messy and labour intensive. My father and brother spent VE day removing the device on the farm truck. They cheerfully paid the price of being forced to use a petrol/kerosene shandy for some years until Prime Minister Ben Chifley removed the rationing system.
A couple of years ago our ABC television station featured a character with a gas producer on his car. He was travelling throughout Australia and thumbing his nose at the need to fill his tank at a service station. However he had to get out occasionally to use a chain saw on roadside logs.
Henry N Broadbent, Somers, Victoria, Australia
Delight at engineering review
How disappointed I was not to be able to forward a submission into the Innovation, Universities and Skills Committee review of UK engineering reported in the 8 March 2008 issue of E&T. As a member of HM Forces, I must take into consideration the environment in which I work and there was not, unfortunately, time to clear my paper.
However, as a general comment I must say how delighted I am at this refreshing new approach to assessing the current state of engineering in the UK. In particular, the area I am interested in is skill fade in the workplace. The decline in numbers within the skilled workforce and the increase in average age, particularly in the nuclear industry, has been of increasing concern since the mid-1990s, or even earlier.
We need a massive educational effort in schools, especially at the GCSE age group, and also at university level, to demonstrate the exciting world that is engineering and the rewards that are on offer. From my own personal experience, I think that as a country, we fail to do this.
I only hope that this review is able to achieve something credible and valuable to the industry. In the meantime I am excited that all parties have fully engaged in the project; I wish it every success.
Ian McNamara MIET, Royal Navy Engineer Officer
Is anybody listening?
I am retired from a family business, established in 1948 and now controlled by my son, where our culture of care for our customer is paramount. We train our own apprentices chosen by those who come to us determined to listen and learn, to be prepared to be punctual, well-mannered, clean and tidy, and all that is required to fit into our culture of care in all that we do.
About 11 years ago I was very aware of the lack of new entrants to our sector. I corresponded with all our trade association with little or no response. I also notified government regarding my concerns. The word 'apprentice' has been taken out of the industry and replaced with NVQs where new entrants were sent to 'training providers'.
During this same period I telephoned the headmaster of a local secondary school. I suggested he send a few pupils to discuss their future plans. Nothing happened! After a couple of months I wrote to the headmaster detailing my concerns for the future of the industry, explaining that plumbing, heating, gas fitting, hot and cold water systems, ventilation, maintenance, drain-age and sewage and electrical elements within the industry are interesting and vital for now and the future and would command good wages, but there was no acknowledgement nor any reply. If a headmaster ignores such helpful and vital correspondence, what is going on?
It is not possible to obtain the necessary skills for our industry in a schoolroom environment; it must be on site, one-to-one, alongside a senior engineer with careful checks to ensure proper progress and external examinations after four years.
Joe Lea MIET, Mawdesley, Nr Ormskirk
Tom Jacobs (Feedback, 8 March 2008) says that DJ Seal "must have had his tongue firmly in his cheek" when recommending lower distribution voltage levels in a letter in an earlier issue.
I can only assume that Mr Jacobs had his own tongue firmly in his cheek. If as he says he was not prepared to change all the cables in his house I would assume that he would not change all the electrical appliances in his house. In that case if the mains voltage were lower so also would be the current drawn by those devices. It is not the declared wattage that determines the current drawn but rather the applied voltage.
Brian Millar, Holywood, Co Down
A banker's view of status
I was interested to read Charles Curry's definition of an engineer (Feedback, 23 February 2008). Perhaps as an engineering graduate turned accountant and banker I can offer an alternative view. I suggest that an engineer should be a manager with a technical training. Sadly, too many engineers are just technicians – highly qualified, but technicians nonetheless. Perhaps that explains the lack of status that your readers frequently bemoan.
Liam O'Keeffe, Abinger Hammer, Surrey
In the 'Less or More' Inventors' Inbox article in the 23 February issue of E&T, Mark Sheahan and Patrick Andrews looked at solutions to getting the last drop of ketchup from a bottle.
With a partially used bottle of ketchup on the dining table, I mentioned to my wife Sheila the problems discussed. Without hesitation, she said the simple solution would be to fit a screw-off bottom to the bottle as well as the screw-off top, but with opposing screw-threads.